[GIS] Custom C# tool populate field combobox parameter from layer parameter

arcobjectscparameters

I'm creating a custom tool for arcmap toolbox where user select FeatureLayer in one combobox, and in next combobox user can select a field from selected FeatureLayer.
FeatureLayer combobox fills automaticaly from:

...
inputParameter.DataType = (IGPDataType)new GPFeatureLayerTypeClass();
inputParameter.Value = (IGPValue)new GPFeatureLayer();

The problem arises when I need to fill field combobox. I'm not realy sure how to set up its parameters. right now i'm trying something like this:

inputParameter = new GPParameterClass();
inputParameter.Enabled = true;
inputParameter.Name = "FieldTrg";
inputParameter.DisplayName = "Feature Class Fields";
inputParameter.Direction = esriGPParameterDirection.esriGPParameterDirectionInput;
inputParameter.ParameterType = esriGPParameterType.esriGPParameterTypeRequired;
inputParameter.DataType = (IGPDataType)new GPStringType();
inputParameter.Value = (IGPValue)new GPString();
//inputParameter.AddDependency("FeatureClassTrg");
//IGPFeatureSchema fgs = new GPFeatureSchemaClass();
//fgs.FieldsRule = esriGPSchemaFieldsType.esriGPSchemaFieldsAll;
//inputParameter.Schema = (IGPSchema)fgs

In UpdateParameters function I were able to get fields in selected FeatureLayer/FeatureClass, but I had no idea where and how should I put them back in combobox.
Also currently the field 'combobox' isn't really a combobox, but just a string field, so probably GPString isn't corect thing to use as its DataType/Value.

Best Answer

As no one have answered this question then i'll share how i managed this. This is part of content in ParameterInfo method.

            inputParameter = new GPParameterClass();
            inputParameter.Enabled = true;
            inputParameter.Name = "myFeatureClass";
            inputParameter.DisplayName = "Targeted Feature Class";
            inputParameter.Direction = esriGPParameterDirection.esriGPParameterDirectionInput;
            inputParameter.ParameterType = esriGPParameterType.esriGPParameterTypeRequired;
            inputParameter.DataType = (IGPDataType)new GPFeatureLayerTypeClass();
            inputParameter.Value = (IGPValue)new GPFeatureLayer();

            _FcTrgID = parameterId++;
            parameters.Add(inputParameter);

            //source field
            inputParameter = new GPParameterClass();
            inputParameter.Enabled = true;
            inputParameter.Name = "myFields";
            inputParameter.DisplayName = "Fields in targeted feature class";
            inputParameter.Direction = esriGPParameterDirection.esriGPParameterDirectionInput;
            inputParameter.ParameterType = esriGPParameterType.esriGPParameterTypeRequired;
            inputParameter.DataType = (IGPDataType)new FieldType();
            inputParameter.Value = (IGPValue)new Field();

            inputParameter.AddDependency("myFeatureClass");
            IGPFeatureSchema trgFS = new GPFeatureSchemaClass();
            trgFS.FieldsRule = esriGPSchemaFieldsType.esriGPSchemaFieldsAll;
            inputParameter.Schema = (IGPSchema)trgFS;

            _FieldTrgID = parameterId++;
            parameters.Add(inputParameter);

And this is par of content in UpdateParameters method

            IGPValue trgParamValue = _GPUtilities.UnpackGPValue(paramvalues.get_Element(_FcTrgID));
            if (trgParamValue.IsEmpty() == false)
            {
                IGPValue tempGPV = new GPFieldInfo();
                IGPParameter3 fieldListParam = (IGPParameter3)paramvalues.get_Element(_FieldTrgID);
                IFeatureClass fc;
                try
                {
                    fc = Helper.getFeatureClass(_GPUtilities, paramvalues, _FcTrgID);
                }
                catch (Exception ex)
                {
                    tempGPV.SetAsText("");
                    _GPUtilities.PackGPValue(tempGPV, fieldListParam);
                    return;
                }
                IFields fields = fc.Fields;

                if (previousTrgFc == fc.AliasName)
                    return;
                previousTrgFc = fc.AliasName;
            }

When ever user change selected FeatureLayer then Field combobox is being refreshed with content of last selected featureLayer fields.

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